From mboxrd@z Thu Jan 1 00:00:00 1970 From: Roman Subject: Firewall with only one eth0 device: possible? Date: Tue, 31 May 2005 18:41:22 +0200 Message-ID: <429C93B2.7040001@gmx.ch> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: netfilter-bounces@lists.netfilter.org Errors-To: netfilter-bounces@lists.netfilter.org Content-Type: text/plain; charset="us-ascii"; format="flowed" To: netfilter@lists.netfilter.org Hi, I have an embedded system running uclinux with just one ethernet device and wonder whether or not I can build a firewall in combination with a switch (VLAN support, not WLAN). How I thought it could work is the following: Configure the eth0 device with an ip and network mask. Configure the eth0:0 alias device with an ip and network mask different from eth0. Use a switch with VLAN support. Connect the eth0 linux device to port B of the switch; switch port A will then be one side of the firewall and port C the other side. Configure the switch (VLAN) in a manner so all the incoming traffic on switch port A will be routed to port B and all the incoming traffic on port B will be routed to port C and back to port A. Finally everything that enters port C will be routed to port B. The question about all this is: Will the traffic be filtered between eth0 and eth0:0 as if there were two physical devices eth0 and eth1? Thanks for any remarks on that. roman PS.: I know, this is an unusual way to build a firewall, but I simply can not change the hardware. For everyone who thinks, it is insecure because of none existing physical separation: please forgive me.